The present invention is directed to adhesive tapes and, more particularly, to providing duct tapes having a lower density and which are consequently more cost-effective to manufacture.
In its simplest form, duct tapes comprise a cloth material carrying an adhesive layer on one surface thereof. While in theory, the adhesive coating could comprise any of the per se known heat--or water-activated adhesives, for ease of application by the user they will usually be one of the known pressure-sensitive adhesives. Useful adhesives for this purpose include acrylic or rubber-based adhesive formulations.
The cloth material employed will preferably be a woven web for ease of tearability in the cross-direction (CD), as distinguished from non-wovens which, due to their primary orientation in the machine direction (MD) are not readily tearable in the CD.
For flexibility as well as the ability to manufacture the tape in roll form, the cloth ordinarily should not have a dense thread count. Consequently, with the woven cloths of lesser thread count density which are employed, the adhesive layer will tend to flow through the cloth, making the resulting product commercially unacceptable.
For this reason, commercially available duct tapes have an outer water-impermeable, flexible plastic laminated to the cloth layer. Since the cloth layer provides reinforcement and increased tensile strength and the backing is of sufficient thickness, e.g. 1-4 mils to provide the requisite dimensional stability, the known duct tapes of this description are characterized as being both strong and flexible.
Manufacturers of these duct tapes are constantly seeking ways to lower the cost of manufacture in order to produce a lower cost duct tape in this highly competitive industry.
A logical way to attempt to do so would be to employ less expensive materials, i.e. less expensive backing materials, cloths and/or adhesives. However, minimal cost savings are obtainable in this manner without sacrificing the qualities of strength, flexibility, and adhesive properties required for the contemplated uses of duct tapes.
Another more viable method of reducing cost is to reduce the density of the tape, namely to reduce the amount of material employed in the manufacture of the tape.
Since the adhesive layer must generally be of a given thickness, e.g. on the order of 1-4 miles to achieve the required adhesive properties for duct tapes and the cloth material is of a given thickness, e.g. 6-10 mils to provide the desired increased tensile strength, in accordance with the present invention efforts to reduce the density were directed to the backing layer itself the major cost item in the current manufacture of duct tapes.
A method of lowering the density of duct tape backings is described and claimed in U.S. Pat. No. 4,705,715 issued to DeCoste and Mamish and assigned to the instant assignee. In accordance with the patented invention the backing for the reinforcing cloth and adhesive layer comprises a layer of plastic foam having a thin plastic skin adhered to the outer surface.
Another way of reducing the material in the backing is to incorporate glass or other such microspheres into said backing.
The present invention is directed to another means of lowering the density of the backing which is easy to manufacture, does not require the use of other materials, e.g. foaming agents, microspheres and the like, and further provides improved adhesive to backing adhesion.